Neurobehavioral function in school-age children exposed to manganese in drinking water

Risks to children from inhalation of aerosolized aqueous manganese emitted from ultrasonic humidifiers can be greater than for corresponding ingestion

The essential trace element manganese (Mn) can cause neurotoxicity with inhalation acknowledged as a more severe health and cognition threat than ingestion.

METHODS

Over a range of aqueous Mn concentrations present in tap water, this research characterizes exposures and risks for adults and 0.25, 1, 2.5, and 6 yr old children who ingest the water and inhale respirable particles produced by a room-sized ultrasonic humidifier filled with the same water. Aqueous Mn concentrations evaluated included 50 µg/L USEPA esthetic guideline, 80 µg/L WHO infant guideline, and 120 µg/L Canadian regulatory level. Airborne-particle-bound Mn concentrations were generated for water filling an ultrasonic humidifier under four realistic room conditions (33 m³ small or 72 m³ large) with varying ventilation rates from 0.2/h -1.5/h. Average daily doses (ADD) and reference intake doses were calculated for ingestion and 8-h inhalation of humidified air. Hazard quotients (HQ) compared the intake doses and reference doses. Multi-path particle dosimetry (MPPD) model quantified the particle deposition and deposited dose in children's and adults' respiratory tracts.

RESULTS

At only 11 µg/L Mn, the resulting humidified air Mn exceeds USEPA's reference concentration of 0.05 µg/m³ Mn in small room with low, energy-efficient ventilation. Inhalation ADD are 2 magnitudes lower than ingestion ADD for identical water Mn concentrations and daily exposure frequency. Even so, ingestion HQs are approximately 0.2 but inhalation risk is significant (HQ>1) for children and adults when breathing Mn-humidified air under most small room conditions at 50, 80 or 120 µg/L Mn. MPPD model indicates inhaled Mn deposits in head and pulmonary regions, with greater Mn dose deposits in children than adults.

CONCLUSION

Inhalation of Mn-particles produced from ultrasonic humidifiers can pose greater risks than ingestion at the same water concentration, especially for children. Aqueous Mn concentration and room size influence risks. Limiting manganese exposures and setting regulations requires consideration of both ingestion and inhalation of water.

Manganese body burden in children is associated with reduced visual motor and attention skills

Manganese (Mn) is an essential element, however, children with moderate to high Mn exposure can exhibit neurobehavioral impairments. One way Mn appears to affect brain function is through altering dopaminergic systems involved with motor and cognitive control including frontal - striatal brain systems. Based on the risk for motor and attention problems, we evaluated neurobehavioral function in 255 children at risk for Mn exposure due to living in proximity to coal ash storage sites. Proton Induced X-ray Emissions (PIXE) analysis was conducted on finger and toenails samples. Multiple neuropsychological tests were completed with the children. Fifty-five children had Mn concentrations above the limit of detection (LOD) (median concentration = 3.95 ppm). Children with detectable Mn concentrations had reduced visual motor skills (β = -5.62, CI: -9.11, -2.12, p = 0.008) and more problems with sustained attention, based on incorrect responses on a computerized attention test, (β = 0.40, CI: 0.21, 0.59, p < 0.001) compared with children who had Mn concentrations below the LOD. Findings suggest that Mn exposure impacts attention and motor control possibly due to neurotoxicity involving basal ganglia and forebrain regions. Visual-motor and attention tests may provide a sensitive measure of Mn neurotoxicity, useful for evaluating the effects of exposure in children and leading to better treatment options.

Manganese Encephalopathy Caused by Homemade Methcathinone (Ephedrone) Prevalence in Poland

Manganese encephalopathy is a known disorder in occupational medicine. A serious phenomenon has been the emergence of manganese encephalopathy in intravenous users of homemade methcathinone (ephedrone). A short survey was developed for clinical environments dealing with people who use psychoactive substances. The data were obtained from 72 rehabilitation therapy centers. Surveys carried out in about a third of Polish centers dealing with providing medical assistance to people addicted to substances other than alcohol and tobacco have shown that over 4% of people treated there had symptoms of manganese encephalopathy, of which more than half are people in whom the probability of a clinical diagnosis of this disorder is significant. It has been shown that knowledge of manganese encephalopathy is none or minimal in more than 70% of the surveyed institutions. An urgent need for personnel training in this field was pointed out. Attention was paid to the importance of disseminating good review articles on new and dynamically developing problem phenomena.

Up-regulation of the manganese transporter SLC30A10 by hypoxia-inducible factors defines a homeostatic response to manganese toxicity

Manganese (Mn) is an essential metal that induces incurable parkinsonism at elevated levels. However, unlike other essential metals, mechanisms that regulate mammalian Mn homeostasis are poorly understood, which has limited therapeutic development. Here, we discovered that the exposure of mice to a translationally relevant oral Mn regimen up-regulated expression of SLC30A10, a critical Mn efflux transporter, in the liver and intestines. Mechanistic studies in cell culture, including primary human hepatocytes, revealed that 1) elevated Mn transcriptionally up-regulated SLC30A10, 2) a hypoxia response element in the SLC30A10 promoter was necessary, 3) the transcriptional activities of hypoxia-inducible factor (HIF) 1 or HIF2 were required and sufficient for the SLC30A10 response, 4) elevated Mn activated HIF1/HIF2 by blocking the prolyl hydroxylation of HIF proteins necessary for their degradation, and 5) blocking the Mn-induced up-regulation of SLC30A10 increased intracellular Mn levels and enhanced Mn toxicity. Finally, prolyl hydroxylase inhibitors that stabilize HIF proteins and are in advanced clinical trials for other diseases reduced intracellular Mn levels and afforded cellular protection against Mn toxicity and also ameliorated the in vivo Mn-induced neuromotor deficits in mice. These findings define a fundamental homeostatic protective response to Mn toxicity-elevated Mn levels activate HIF1 and HIF2 to up-regulate SLC30A10, which in turn reduces cellular and organismal Mn levels, and further indicate that it may be possible to repurpose prolyl hydroxylase inhibitors for the management of Mn neurotoxicity.

Chronic Manganese Exposure and the Enteric Nervous System: An in Vitro and Mouse in Vivo Study

BACKGROUND

Chronic environmental exposure to manganese (Mn) can cause debilitating damage to the central nervous system. However, its potential toxic effects on the enteric nervous system (ENS) have yet to be assessed.

OBJECTIVE

We examined the effect of Mn on the ENS using both cell and animal models.

METHOD

Rat enteric glial cells (EGCs) and mouse primary enteric cultures were exposed to increasing concentrations of Mn and cell viability and mitochondrial health were assessed using various morphological and functional assays. C57BL/6 mice were exposed daily to a sublethal dose of Mn (15mg/kg/d) for 30 d. Gut peristalsis, enteric inflammation, gut microbiome profile, and fecal metabolite composition were assessed at the end of exposure.

RESULTS

EGC mitochondria were highly susceptible to Mn neurotoxicity, as evidenced by lower mitochondrial mass, adenosine triphosphate-linked respiration, and aconitase activity as well as higher mitochondrial superoxide, upon Mn exposure. Minor differences were seen in the mouse model: specifically, longer intestinal transit times and higher levels of colonic inflammation.

CONCLUSION

Based on our findings from this study, Mn preferentially induced mitochondrial dysfunction in a rat EGC line and in vivo resulted in inflammation in the ENS. https://doi.org/10.1289/EHP7877.

Nail Samples of Children Living near Coal Ash Storage Facilities Suggest Fly Ash Exposure and Elevated Concentrations of Metal(loid)s

Children who live near coal-fired power plants are exposed to coal fly ash, which is stored in landfills and surface impoundments near residential communities. Fly ash has the potential to be released as fugitive dust. Using data collected from 263 children living within 10 miles of coal ash storage facilities in Jefferson and Bullitt Counties, Kentucky, USA, we quantified the elements found in nail samples. Furthermore, using principal component analysis (PCA), we investigated whether metal(loid)s that are predominately found in fly ash loaded together to indicate potential exposure to fly ash. Concentrations of several neurotoxic metal(loid)s, such as chromium, manganese, and zinc, were higher than concentrations reported in other studies of both healthy and environmentally exposed children. From PCA, it was determined that iron, aluminum, and silicon in fly ash were found to load together in the nails of children living near coal ash storage facilities. These metal(loid)s were also highly correlated with each other. Last, results of geospatial analyses partially validated our hypothesis that children's proximity to power plants was associated with elevated levels of concentrations of fly ash metal(loid)s in nails. Taken together, nail samples may be a powerful tool in detecting exposure to fly ash.

Hair levels of heavy metals and essential elements in Chinese children with autism spectrum disorder

BACKGROUND

Disproportional heavy metals and essential elements were reported in children with autism spectrum disorder (ASD) that is obscure in etiology. Inevitably, the association is biased by diet and environmental factors.

METHODS

Fifty pairs, one with ASD and the other living together from the same special school with cerebral palsy (CP), were recruited in Hangzhou (China), aged from 2 to 11 years old (74.0 % male). All samples were divided into two subgroups: preschool-aged (2-5 years old) and school-aged (6-10 years old). Heavy metals (As, Hg, Pb) and essential elements (Al, Ca, Cu, Mg, Mn, Zn) in hair were quantified by inductively coupled plasma mass spectrometry analysis and flame atomic absorption spectroscopy.

RESULTS

The children with ASD generally had lower hair levels of Mn (ASD 0.124 μg/g, CP 0.332 μg/g, P = 0.001) compared to the children with CP. After stratification for age, there were no significant differences detected in preschool-aged group. In school-aged group, the results exhibited the children with ASD had higher hair Pb (1.485 μg/g, 0.690 μg/g, P = 0.007) and Cu/Zn ratio (0.092, 0.060, P = 0.003), while hair Hg (0.254 μg/g, 0.353 μg/g, P = 0.016)、Mn (0.089 μg/g, 0.385 μg/g, P = 0.002)、Mg (17.81 μg/g, 24.53 μg/g, P = 0.014) and Zn (100.15 μg/g, 135.83 μg/g, P = 0.007) showed an opposite pattern.

CONCLUSIONS

These results suggest an imbalance of Mn in Chinese children with ASD.

Comparations of major and trace elements in soil, water and residents' hair between longevity and non-longevity areas in Bama, China

Natural environment is an important factor affecting longevity. Soil, water and hair samples from Bama were assayed to investigate the effects of elements on the regional longevity. The concentrations of Cd, Co and Mg in soil and Co in drinking water were significantly higher in longevity area than those in non-longevity area (p < 0.05). The concentrations of K, Mo, Na, Pb and V in soil, Mg, Na, Fe, Li and Mn in drinking water and I, K, Mg, Mn, Na and Sr in hair were significantly lower in longevity area than those in non-longevity area (p < 0.05). Mg, Mn, Na and Sr in hair were affected by soil and drinking water. Our results indicate that adequate concentration of Mg in soil might benefit longevity, excessive concentrations of Na in soil, Mg, Mn and Na in drinking water and Mg, Mn, Na and Sr in hair might reduce lifespan of local residents.

Prenatal manganese serum levels and neurodevelopment at 4 years of age

BACKGROUND

The excess of manganese (Mn) causes severe deleterious effects in the central nervous system, and the developing brain is especially sensitive to Mn overload. However, results of prospective studies regarding Mn neurodevelopmental effects remain inconclusive. The present study aims at studying the association of prenatal Mn exposure and neurodevelopment at 4-5 years of age.

METHODS

Mn serum concentration was measured in 1465 pregnant women from the INMA (INfancia y MedioAmbiente, Environment and Childhood) Project. Neurodevelopment was assessed using a standardized version of the McCarthy Scales of Children's Abilities (MSCA). Multivariate regression models were used for data analysis.

RESULTS

No association was found between Mn levels in serum and any of the McCarthy scales. However, the stratification by sex showed a positive and beneficial association of prenatal Mn levels and the verbal, quantitative and general-cognitive scales in girls (β (95%CI): 4 (0.03, 7.96), 4.5 (0.43, 8.57) and 4.32 (0.6, 8.05), respectively).

CONCLUSIONS

A beneficial association was found for the first time between prenatal Mn levels measured in serum and neurodevelopment of female offspring at 4 years of age, which could have implications on public health policies, specifically on the establishment of policies promoting prenatal health related to dietary deficits of micronutrients such as Mn.

Evaluating the risk of manganese-induced neurotoxicity of parenteral nutrition: review of the current literature

INTRODUCTION

Several diseases and clinical conditions can affect enteral nutrition and adequate gastrointestinal uptake. In this respect, parenteral nutrition (PN) is necessary for the provision of deficient trace elements. However, some essential elements, such as manganese (Mn) may be toxic to children and adults when parenterally administered in excess, leading to toxic, especially neurotoxic effects.

AREAS COVERED

Here, we briefly provide an overview on Mn, addressing its sources of exposure, the role of Mn in the etiology of neurodegenerative diseases, and focusing on potential mechanisms associated with Mn-induced neurotoxicity. In addition, we discuss the potential consequences of overexposure to Mn inherent to PN.

EXPERT OPINION

In this critical review, we suggest that additional research is required to safely set Mn levels in PN, and that eliminating Mn as an additive should be considered by physicians and nutritionists on a case by case basis in the meantime to avoid the greater risk of neurotoxicity by its presence. There is a need to better define clinical biomarkers for Mn toxicity by PN, as well as identify new effective agents to treat Mn-neurotoxicity. Moreover, we highlight the importance of the development of new guidelines and practice safeguards to protect patients from excessive Mn exposure and neurotoxicity upon PN administration.

Chemical and in vitro bioanalytical assessment of drinking water quality in Manhiça, Mozambique

BACKGROUND

The chemical quality of drinking water is widely unknown in low-income countries.

OBJECTIVE

We conducted an exploratory study in Manhiça district (Mozambique) to evaluate drinking water quality using chemical analyses and cell-based assays.

METHODS

We measured nitrate, fluoride, metals, pesticides, disinfection by-products, and industrial organochlorinated chemicals, and conducted the bioassays Ames test for mutagenicity, micronuclei assay (MN-FACS), ER-CALUX, and antiAR-CALUX in 20 water samples from protected and unprotected sources.

RESULTS

Nitrate was present in all samples (median 7.5 mg/L). Manganese, cobalt, chromium, aluminium, and barium were present in 90-100% of the samples, with median values of 32, 0.6, 2.0, 61, 250 μg/l, respectively. Manganese was above 50 μg/l (EU guideline) in eight samples. Arsenic, lead, nickel, iron, and selenium median values were below the quantification limit. Antimony, cadmium, copper, mercury, zinc and silver were not present. Trihalomethanes, haloacetic acids, haloacetonitriles and haloketones were present in 5-28% samples at levels ≤4.6 μg/l. DDT, dieldrin, diuron, and pirimiphos-methyl were quantified in 2, 3, 3, and 1 sample, respectively (range 12-60 ng/L). Fluoride was present in one sample (0.11 mg/l). Trichloroethene and tetrachloroethene were not present. Samples were negative in the in vitro assays.

SIGNIFICANCE

Results suggest low exposure to chemicals, mutagenicity, genotoxicity and endocrine disruption through drinking water in Manhiça population. High concentration of manganese in some samples warrants confirmatory studies, given the potential link to impaired neurodevelopment.

Previously unrecognized potential threat to children from manganese in groundwater in rohingya refugee camps in Cox's Bazar, Bangladesh

The forced displacement of over 700,000 Rohingyas from Myanmar to Bangladesh since the crackdown in August 2017 has resulted in a critical humanitarian and environmental crisis. Groundwater is the primary source of drinking water in the camps that were constructed to provide shelter for the refugee population. The current study explores occurrence of Mn in groundwater in the Rohingya camps and adjacent areas. A total of 52 groundwater samples were collected between August and October 2018 from different camps sites and the adjacent host area. It was found that 64% exceeded the Bangladesh standard (100 μg/L) suggesting the presence of elevated concentrations of Mn in some groundwater aquifers in the camp sites. Mn is a neurotoxicant and previous studies have reported intellectual impairment in children exposed to Mn levels similar to those detected in groundwater in the camp sites. Nearly 450,000 migrant and new-born children live in the camps in already stressed conditions. The occurrence of elevated Mn concentrations in groundwater in the camps and their adjacent areas is likely an additional stressor exposing these children to an increased risk of neurotoxicity. Based on the results of this small-scale study, we recommend undertaking an in-depth study on the occurrence of Mn in groundwater in the camps to come up with appropriate strategies to minimise exposure. In addition, we recommend conducting a systematic epidemiological study on potential impacts of manganese in drinking water on neurological development of the Rohingya children in the camps.

Variation in groundwater manganese in Finland

Increasing evidence has emerged that Mn derived from drinking water could be a health risk, especially for children. This study aimed to provide more information on the variation in Mn concentrations in well water and factors that affect manganese concentrations in groundwater in the natural environment. The geochemical data consisted of analyses of single water samples (n = 5311) that were taken only once and data from monitoring sites where water samples (n = 4607) were repeatedly taken and analyzed annually from the same wells. In addition, the well-specific results from six wells at monitoring sites were described in detail. We obtained the data on water samples from the groundwater database of Geological Survey of Finland. In single samples, Mn concentrations varied from < 0.02 µg/l to 5800 µg/l in bedrock well waters and up to 6560 µg/l in Quaternary deposit well waters. Results from single water samples from bedrock wells and Quaternary deposit wells indicated that the dissolved oxygen content has an inverse association with the Mn concentration. When the dissolved oxygen O₂ levels were lower, the Mn concentrations were higher. No clear association was found between the Mn concentration and the pH or depth of the well for single samples. Part of Mn was particle bound, because total Mn was higher than soluble Mn in most measured samples. In the monitoring survey, large variation in Mn concentrations was found in bedrock well water in Kemijärvi, 114-352 µg/l, and in dug well water in Hämeenkoski, 8.77-2640 µg/l. Seasonal and spatial variability in Mn concentrations in water samples from two bedrock wells was large at monitoring sites in northern Finland. Variability in the Mn concentrations in groundwater can be large, even in the same area. These data suggest that single measurements of the Mn concentration from a water source may not reveal the Mn status, and measurement of both the total and soluble Mn concentrations may be recommended.

Associations of metals and neurodevelopment: a review of recent evidence on susceptibility factors

PURPOSE OF REVIEW

Epidemiologic evidence exists that many metals are associated with adverse neurobehavioral effects in young children, including lead (Pb), methylmercury (meHg), manganese (Mn) and arsenic (As)5-8. Importantly, chemical insult can vary depending on host factors and exposure circumstance. This systematic review summarizes the recent literature investigating modifying factors of the associations between metals and neurodevelopment, including immutable traits (sex or genetics) or exposure conditions (timing or co-exposures).

RECENT FINDINGS

Of the 53 studies included in this review, the number investigating modification of exposure effects were: 30 for sex, 21 for co-exposures, 12 for timing of exposure, and six for genetic modifiers. Sex-specific effects of metal-neurobehavioral associations were inconclusive for all metals, likely due to the heterogeneity of outcome domains assessed and the exposure time points measured. Seven studies evaluated both sex and exposure timing as modifying factors using deciduous teeth or other biomarkers with repeated measures to characterize metals exposure over time. Only five studies used statistical methods for mixtures to evaluate associations of more than two metals with neurobehavioral domains.

SUMMARY

Despite the expansion of research on susceptibility to the neurodevelopmental effects of metals exposure, considerable gaps remain. This work remains critical, as characterizing susceptible subpopulations can aid in identifying biological mechanisms and is fundamental for the protection of public health.

Is direct-drinking water safe for children? An analysis of direct-drinking water quality and its risk factors in Shanghai elementary and middle schools

BACKGROUND

Drinking water quality for children should be higher than adults due to both behavioral and physiological factors. Thus, to provide enough, safe, and easily accessible drinking water for children at schools, the Shanghai Municipal Government initiated a direct-drinking water project in 2013. However, there has been no study so far to assess the quality of direct-drinking water or to investigate its risk factors in Shanghai elementary and middle schools.

METHODS

In the present study, we selected direct-drinking water equipment from 183 elementary and middle schools (17% of total) in Shanghai to detect the colony-forming units (CFU), residual chlorine, chemical oxygen demand (COD), and turbidity of water samples, and analyzed the risk factors of its quality using both simple and multiple linear regression analysis.

RESULTS

Results showed that the CFU, residual chlorine, COD, and turbidity of direct-drinking water in Shanghai elementary and middle schools ranged from <LOD->300 cfu/mL, <LOD-0.670 mg/L, 0.090-2.710 mg/L, and 0.100-2.050 NTU, respectively. The results of simple linear regression analysis indicated that the CFU of direct-drinking water significantly increased when water temperature was between 25 and 60 °C (β = 19.862, p = 0.030), but it was decreased at 60-100 °C (β = - 16.387, p = 0.046). Additionally, the CFU was higher in elementary schools than middle schools, which was also affected by faucet type and water treatment technology (p = 0.006, 0.012 and 0.042, respectively). The residual chlorine in direct-drinking water significantly increased when there was no toilet within 10 m (β = 0.012, p = 0.045). The COD of direct-drinking water was significantly higher in rural areas and in warm water, compared to urban areas (p = 0.033) and room temperature water (p = 0.000), respectively. The turbidity of direct-drinking water was significantly higher in urban areas and water using UF/MF technology, compared to rural areas (p = 0.030) and RO technology (p = 0.009), respectively. The results of multiple linear regressions analysis drew the same conclusions.

CONCLUSIONS

In order to improve the quality of direct-drinking water, the equipment should be as far away from toilet as possible and direct-drinking water should be kept at room temperature or heated at high temperature (over 60 °C). Furthermore, sanitary standards of direct-drinking water quality and relevant laws and regulations should be established and implemented as soon as possible. Our study demonstrates that it is critical to improve direct-drinking water quality and ensure the safety of drinking water in elementary and middle schools in Shanghai.

Manganese-induced neurodegenerative diseases and possible therapeutic approaches

INTRODUCTION

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and prion disease represent important public health concerns. Exposure to high levels of  heavy metals such as manganese (Mn) may contribute to their development.

AREAS COVERED

In this critical review, we address the role of Mn in the etiology of neurodegenerative diseases and discuss emerging treatments of Mn overload, such as chelation therapy. In addition, we discuss natural and synthetic compounds under development as prospective therapeutics. Moreover, bioinformatic approaches to identify new potential targets and therapeutic substances to reverse the neurodegenerative diseases are discussed.

EXPERT OPINION

Here, the authors highlight the importance of better understanding the molecular mechanisms of toxicity associated with neurodegenerative diseases, and the role of Mn in these diseases. Additional emphasis should be directed to the discovery of new agents to treat Mn-induced diseases, since present day chelator therapies have limited bioavailability. Furthermore, the authors encourage the scientific community to develop research using libraries of compounds to screen those compounds that show efficacy in regulating brain Mn levels. In addition, bioinformatics may provide novel insight for pathways and clinical treatments associated with Mn-induced neurodegeneration, leading to a new direction in Mn toxicological research.

Biomarkers of environmental manganese exposure and associations with childhood neurodevelopment: a systematic review and meta-analysis

BACKGROUND

Although prior studies showed a correlation between environmental manganese (Mn) exposure and neurodevelopmental disorders in children, the results have been inconclusive. There has yet been no consistent biomarker of environmental Mn exposure. Here, we summarized studies that investigated associations between manganese in biomarkers and childhood neurodevelopment and suggest a reliable biomarker.

METHODS

We searched PubMed and Web of Science for potentially relevant articles published until December 31th 2019 in English. We also conducted a meta-analysis to quantify the effects of manganese exposure on Intelligence Quotient (IQ) and the correlations of manganese in different indicators.

RESULTS

Of 1754 citations identified, 55 studies with 13,388 subjects were included. Evidence from cohort studies found that higher manganese exposure had a negative effect on neurodevelopment, mostly influencing cognitive and motor skills in children under 6 years of age, as indicated by various metrics. Results from cross-sectional studies revealed that elevated Mn in hair (H-Mn) and drinking water (W-Mn), but not blood (B-Mn) or teeth (T-Mn), were associated with poorer cognitive and behavioral performance in children aged 6-18 years old. Of these cross-sectional studies, most papers reported that the mean of H-Mn was more than 0.55 μg/g. The meta-analysis concerning H-Mn suggested that a 10-fold increase in hair manganese was associated with a decrease of 2.51 points (95% confidence interval (CI), - 4.58, - 0.45) in Full Scale IQ, while the meta-analysis of B-Mn and W-Mn generated no such significant effects. The pooled correlation analysis revealed that H-Mn showed a more consistent correlation with W-Mn than B-Mn. Results regarding sex differences of manganese associations were inconsistent, although the preliminary meta-analysis found that higher W-Mn was associated with better Performance IQ only in boys, at a relatively low water manganese concentrations (most below 50 μg/L).

CONCLUSIONS

Higher manganese exposure is adversely associated with childhood neurodevelopment. Hair is the most reliable indicator of manganese exposure for children at 6-18 years of age. Analysis of the publications demonstrated sex differences in neurodevelopment upon manganese exposure, although a clear pattern has not yet been elucidated for this facet of our study.

Manganese, Arsenic, and Carbonate Interactions in Model Oxic Groundwater Systems

Manganese and arsenic both threaten groundwater quality globally, but their chemical behavior leads to both co-contamination and separation of these contaminants from individual well to regional scales. Here we tested manganese and arsenic retention under conditions commonly found within aquifer redox fluctuating and transition zones where both arsenic and iron phases are present in oxidized forms, but manganese persists as reduced and soluble Mn(II). Analysis of column aqueous breakthrough data and characterization of solid-phase products using X-ray photoelectron (XPS) and absorption spectroscopies (XAS) show that the addition of bicarbonate increased manganese retention but decreased arsenic retention, while the presence of manganese and arsenic together increased both arsenic and manganese retention. In the presence of O₂ arsenic remained oxidized as arsenate under all conditions measured; however, reduced Mn(II) was oxidized to an average Mn oxidation state of ∼3 in the absence of arsenate. The presence of arsenate partially inhibited Mn(II) oxidation likely by blocking ferrihydrite surfaces needed to catalyze Mn(II) oxidation by O₂ and by stabilizing Mn(II) via ternary complex formation. These results highlight the interactions between reduced and oxidized contaminants that can contribute to the co-occurrence or physical separation of manganese and arsenic in groundwater systems under changing or stratified redox conditions.

Exposure to Manganese in Drinking Water during Childhood and Association with Attention-Deficit Hyperactivity Disorder: A Nationwide Cohort Study

BACKGROUND

Manganese (Mn) in drinking water may increase the risk of several neurodevelopmental outcomes, including attention-deficit hyperactivity disorder (ADHD). Earlier epidemiological studies on associations between Mn exposure and ADHD-related outcomes had small sample sizes, lacked spatiotemporal exposure assessment, and relied on questionnaire data (not diagnoses)-shortcomings that we address here.

OBJECTIVE

Our objective was to assess the association between exposure to Mn in drinking water during childhood and later development of ADHD.

METHODS

In a nationwide population-based registry study in Denmark, we followed a cohort of 643,401 children born 1992-2007 for clinical diagnoses of ADHD. In subanalyses, we classified cases into ADHD-Inattentive and ADHD-Combined subtypes based on hierarchical categorization of International Classification of Diseases (ICD)-10 codes. We obtained Mn measurements from 82,574 drinking water samples to estimate longitudinal exposure during the first 5 y of life with high spatiotemporal resolution. We modeled exposure as both peak concentration and time-weighted average. We estimated sex-specific hazard ratios (HRs) in Cox proportional hazards models adjusted for age, birth year, socioeconomic status (SES), and urbanicity.

RESULTS

We found that exposure to increasing levels of Mn in drinking water was associated with an increased risk of ADHD-Inattentive subtype, but not ADHD-Combined subtype. After adjusting for age, birth year, and SES, females exposed to high levels of Mn (i.e., >100μg/L) at least once during their first 5 y of life had an HR for ADHD-Inattentive subtype of 1.51 [95% confidence interval (CI): 1.18, 1.93] and males of 1.20 (95% CI: 1.01, 1.42) when compared with same-sex individuals exposed to <5μg/L. When modeling exposure as a time-weighted average, sex differences were no longer present.

DISCUSSION

Mn in drinking water was associated with ADHD, specifically the ADHD-Inattentive subtype. Our results support earlier studies suggesting a need for a formal health-based drinking water guideline value for Mn. Future Mn-studies should examine ADHD subtype-specific associations and utilize direct subtype measurements rather than relying on ICD-10 codes alone. https://doi.org/10.1289/EHP6391.

Dysregulation of TFEB contributes to manganese-induced autophagic failure and mitochondrial dysfunction in astrocytes

Epidemiological and clinical studies have long shown that exposure to high levels of heavy metals are associated with increased risks of neurodegenerative diseases. It is widely accepted that autophagic dysfunction is involved in pathogenesis of various neurodegenerative disorders; however, the role of heavy metals in regulation of macroautophagy/autophagy is unclear. Here, we show that manganese (Mn) induces a decline in nuclear localization of TFEB (transcription factor EB), a master regulator of the autophagy-lysosome pathway, leading to autophagic dysfunction in astrocytes of mouse striatum. We further show that Mn exposure suppresses autophagic-lysosomal degradation of mitochondria and induces accumulation of unhealthy mitochondria. Activation of autophagy by rapamycin or TFEB overexpression ameliorates Mn-induced mitochondrial respiratory dysfunction and reactive oxygen species (ROS) generation in astrocytes, suggesting a causal relation between autophagic failure and mitochondrial dysfunction in Mn toxicity. Taken together, our data demonstrate that Mn inhibits TFEB activity, leading to impaired autophagy that is causally related to mitochondrial dysfunction in astrocytes. These findings reveal a previously unappreciated role for Mn in dysregulation of autophagy and identify TFEB as a potential therapeutic target to mitigate Mn toxicity.

ABBREVIATIONS

BECN1: beclin 1; CTSD: cathepsin D; DMEM: Dulbecco's Modified Eagle Medium; GFAP: glial fibrillary acid protein; GFP: green fluorescent protein; HBSS: hanks balanced salt solution; LAMP: lysosomal-associated membrane protein; LDH: lactate dehydrogenase; Lys Inh: lysosomal inhibitors; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAPK: mitogen-activated protein kinase; Mn: manganese; MTOR: mechanistic target of rapamycin kinase; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; PFA: paraformaldehyde; PI: propidium iodide; ROS: reactive oxygen species; s.c.: subcutaneous; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy; TFEB: transcription factor EB.

Early postnatal manganese exposure causes arousal dysregulation and lasting hypofunctioning of the prefrontal cortex catecholaminergic systems

Studies have reported associations between environmental manganese (Mn) exposure and impaired cognition, attention, impulse control, and fine motor function in children. Our recent rodent studies established that elevated Mn exposure causes these impairments. Here, rats were exposed orally to 0, 25, or 50 mg Mn kg-1  day-1 during early postnatal life (PND 1-21) or lifelong to determine whether early life Mn exposure causes heightened behavioral reactivity in the open field, lasting changes in the catecholaminergic systems in the medial prefrontal cortex (mPFC), altered dendritic spine density, and whether lifelong exposure exacerbates these effects. We also assessed astrocyte reactivity (glial fibrillary acidic protein, GFAP), and astrocyte complement C3 and S100A10 protein levels as markers of A1 proinflammatory or A2 anti-inflammatory reactive astrocytes. Postnatal Mn exposure caused heightened behavioral reactivity during the first 5-10 min intervals of daily open field test sessions, consistent with impairments in arousal regulation. Mn exposure reduced the evoked release of norepinephrine (NE) and caused decreased protein levels of tyrosine hydroxylase (TH), dopamine (DA) and NE transporters, and DA D1 receptors, along with increased DA D2 receptors. Mn also caused a lasting increase in reactive astrocytes (GFAP) exhibiting increased A1 and A2 phenotypes, with a greater induction of the A1 proinflammatory phenotype. These results demonstrate that early life Mn exposure causes broad lasting hypofunctioning of the mPFC catecholaminergic systems, consistent with the impaired arousal regulation, attention, impulse control, and fine motor function reported in these animals, suggesting that mPFC catecholaminergic dysfunction may underlie similar impairments reported in Mn-exposed children.

Maintaining Translational Relevance in Animal Models of Manganese Neurotoxicity

Manganese is an essential metal, but elevated brain Mn concentrations produce a parkinsonian-like movement disorder in adults and fine motor, attentional, cognitive, and intellectual deficits in children. Human Mn neurotoxicity occurs owing to elevated exposure from occupational or environmental sources, defective excretion (e.g., due to cirrhosis), or loss-of-function mutations in the Mn transporters solute carrier family 30 member 10 or solute carrier family 39 member 14. Animal models are essential to study Mn neurotoxicity, but in order to be translationally relevant, such models should utilize environmentally relevant Mn exposure regimens that reproduce changes in brain Mn concentrations and neurological function evident in human patients. Here, we provide guidelines for Mn exposure in mice, rats, nematodes, and zebrafish so that brain Mn concentrations and neurobehavioral sequelae remain directly relatable to the human phenotype.

Brain manganese and the balance between essential roles and neurotoxicity

Manganese (Mn) is an essential micronutrient required for the normal development of many organs, including the brain. Although its roles as a cofactor in several enzymes and in maintaining optimal physiology are well-known, the overall biological functions of Mn are rather poorly understood. Alterations in body Mn status are associated with altered neuronal physiology and cognition in humans, and either overexposure or (more rarely) insufficiency can cause neurological dysfunction. The resultant balancing act can be viewed as a hormetic U-shaped relationship for biological Mn status and optimal brain health, with changes in the brain leading to physiological effects throughout the body and vice versa. This review discusses Mn homeostasis, biomarkers, molecular mechanisms of cellular transport, and neuropathological changes associated with disruptions of Mn homeostasis, especially in its excess, and identifies gaps in our understanding of the molecular and biochemical mechanisms underlying Mn homeostasis and neurotoxicity.

Parkinsonism and chronic manganese exposure: Pilot study with clinical, environmental and experimental evidence

Parkinsonism related to chronic Manganese exposure is notably due to focal lesions of the basal ganglia. Our study focused on epidemiological, clinical, toxicological and experimental aspects of Manganese-induced Parkinsonism in south of Morocco. It is a prospective study concerning the workers and the residents bordering on the 2 mines in the south of Morocco. The results of the study concerned 120 cases divided into 4 groups of patients: G1: 30 cases exposed to different incriminated toxic products, which present Parkinsonian signs, G2: 30 cases healthy and exposed, G3: 30 cases affected with Idiopathic Parkinson's disease, and G4: 30 cases healthy and unexposed (controls).

The results from the first mine show that 5.7% of the sample developed Manganese-Induced Parkinsonism and this percentage is slightly higher (4.5%) than the second mine site. Chemical and biological analysis revealed high levels of Manganese. The majority of patients did not improve the clinical signs under L-dopa treatment. The authors underline the gravity of Manganese-induced Parkinsonism and propose a listing of the various exposures as well as a cartography of the regions of risk in Morocco.

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The objective of this study was to update the data about Manganese-Induced Parkinsonism in the South of Morocco.

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Multidisciplinary study putting together clinicians, biologists, biochemists, and pathologists to map accurately areas of exposure to heavy metals.

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Specific considerations should be taken concerning miners by improving work conditions and obliging the use of protective equipment.

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General approach on primary prevention for the population living near the mines in the way to decrease the number of cases.

The effects of manganese overexposure on brain health

Manganese (Mn) is the twelfth most abundant element on the earth and an essential metal to human health. Mn is present at low concentrations in a variety of dietary sources, which provides adequate Mn content to sustain support various physiological processes in the human body. However, with the rise of Mn utility in a variety of industries, there is an increased risk of overexposure to this transition metal, which can have neurotoxic consequences. This risk includes occupational exposure of Mn to workers as well as overall increased Mn pollution affecting the general public. Here, we review exposure due to air pollution and inhalation in industrial settings; we also delve into the toxic effects of manganese on the brain such as oxidative stress, inflammatory response and transporter dysregulation. Additionally, we summarize current understandings underlying the mechanisms of Mn toxicity.

The Relationship between Selected Bioelements and Depressiveness Associated with Testosterone Deficiency Syndrome in Aging Men

Background and Objectives: Abnormal concentrations of bioelements (magnesium, manganese, chromium, copper, zinc) have been associated with physical and emotional dysfunctions, including depression. This association, however, has not been analyzed in testosterone deficiency syndrome (TDS) or patients with depressiveness, i.e., when individual symptoms do not form the picture of a full-syndrome depressive disorder. This study aimed to assess the relationship between concentrations of selected bioelements and the incidence of depressive symptoms in men aged 50 years and older with a concurrent testosterone deficiency syndrome. Material and Methods: Blood samples were taken from 314 men; the mean age of the population was 61.36 ± 6.38 years. Spectrophotometric method for biochemical analysis of magnesium (Mg), manganese (Mn), chromium (Cr), copper (Cu), and zinc (Zn) was used. The diagnosis of testosterone deficiency syndrome (TDS) was based on the total testosterone (TT), free testosterone (FT), estradiol (E2), and dehydroepiandrosterone sulfate (DHEAS) levels by ELISA. Each participant completed the Androgen Deficiency in Aging Male (ADAM) questionnaire, as well as the Beck Depression Inventory (BDI-Ia) measuring the severity of depressive symptoms. Results: Emotional disturbances manifested as depressive symptoms were diagnosed in 28.7% of all participants and testosterone deficiency syndrome in 49.3%. In the TDS group, the analysis showed a significant correlation between the level of manganese (R = 0.225, p = 0.005) and chromium (R = 0.185, p = 0.021) with the incidence of depression. Conclusions: The results of our study demonstrated a relationship between manganese and chromium concentrations with the incidence of depression in men aged 50 years and older with a concurrent testosterone deficiency syndrome. This may indicate that there is a correlation between these bioelements, as well as emotional disorders manifested as depressive symptoms in aging men with a diagnosed testosterone deficiency.

Prenatal Manganese Exposure and Long-Term Neuropsychological Development at 4 Years of Age in a Population-Based Birth Cohort

Background: Manganese (Mn) is an essential micronutrient for humans, the diet being the main source of exposure. Some epidemiological studies describe a negative association between prenatal Mn and later neuropsychological development, but results are inconsistent. The aim of this study was to explore the association between prenatal Mn exposure and neuropsychological development assessed at 4 years of age. Methods: Study subjects were 304 mother-child pairs from the Gipuzkoa cohort of the INMA (Environment and Childhood) Project. Mn was measured in newborns’ hair. Children’s neuropsychological development was assessed at 4 years of age using the McCarthy Scales of Children’s Abilities. Multivariate linear regression models were built. Stratified analysis by sex was performed. Generalized additive models were used to assess the shape of the relation. Results: The median Mn concentration in newborns’ hair was 0.42 μg/g (95% CI = 0.38, 0.46). The association between Mn levels and the neuropsychological development was not statistically significant for the general cognitive scale (β [95% CI] = 0.36 [−5.23, 5.95]), motor scale (β [95% CI] = 1.9 [−3.74, 7.55]) or any of the other outcomes. No sex-specific pattern was found. The best shape describing the relationship was linear for all the scales. Conclusion: Our results suggest that prenatal Mn concentrations measured in newborns’ hair do not affect cognitive or motor development at 4 years of age in boys or in girls at the observed Mn levels.

Source Water Characteristics and Building-specific Factors Influence Corrosion and Point of Use Water Quality in a Decentralized Arctic Drinking Water System

Access to clean and safe drinking water is a perpetual concern in Arctic communities because of challenging climatic conditions, limited options for the transportation of equipment and process chemicals, and the ongoing effects of colonialism. Water samples were gathered from multiple locations in a decentralized trucked drinking water system in Nunavut, Canada, over the course of one year. The results indicate that point of use drinking water quality was impacted by conditions in the source water and in individual buildings and strongly suggest that lead and copper measured at the tap were related to corrosion of onsite premise plumbing components. Humic-like substances were the dominant organic fraction in all samples, as determined by regional integration of fluorescence data. Iron and manganese levels in the source water and throughout the water system were higher in the winter and lower in the summer months. Elevated concentrations of copper (>2000 μg L^-1) and lead (>5 μg L^-1) were detected in tap water from some buildings. Field flow fractionation coupled with inductively coupled plasma mass spectrometry and ultraviolet-visible spectrometry was used to demonstrate the link between source water characteristics (high organics, iron and manganese) and lead and copper in point of use drinking water.

A systematic review and meta-analysis examining the interrelationships between chemical and non-chemical stressors and inherent characteristics in children with ADHD

Children may be more vulnerable to the combined interactions of chemical and non-chemical stressors from their built, natural, and social environments when compared to adults. Attention deficit/hyperactivity disorder (ADHD) is the most commonly diagnosed childhood neurodevelopmental disorder and is considered a major public health issue, as 75% of childhood cases persist into adulthood. ADHD is characterized by developmentally inappropriate levels of hyperactivity, impulsivity, and inattention, with the neurotransmitter serotonin regulating these symptoms. Monoamine oxidase A (MAOA) aids in serotonin uptake and is often implicated in behavioral and emotional disorders, including ADHD. When children are exposed to cigarette smoke, bisphenol A (BPA), or organophosphate pesticides, MAOA activity is inhibited. Non-chemical stressors, such as traumatic childhood experiences, and lifestyle factors, complicate the relationship between genotype and exposures to chemical stressors. But the co-occurrence among outcomes between exposures to chemical stressors, non-chemical stressors, and the low activity MAOA genotype suggest that mental illness in children may be influenced by multiple interacting factors. In this systematic review, we examine the existing literature that combines exposures to chemical and non-chemical stressors (specifically childhood trauma), MAOA characteristics, and ADHD diagnosis to investigate the interrelationships present. We observe that chemical (lead [Pb], phthalates/plasticizers, persistent organic pollutants, and cigarette smoke) exposure is significantly related to ADHD in children. We also observed that existing literature examining the interaction between MAOA, exposures to chemical stressors, and traumatic experiences and their effect on ADHD outcomes is sparse. We recommend that future studies investigating childhood ADHD include chemical and non-chemical stressors and inherent characteristics to gain a holistic understanding of childhood mental health outcomes.

A benchmark concentration analysis for manganese in drinking water and IQ deficits in children

BACKGROUND

Manganese is an essential nutrient, but in excess, can be a potent neurotoxicant. We previously reported findings from two cross-sectional studies on children, showing that higher concentrations of manganese in drinking water were associated with deficits in IQ scores. Despite the common occurrence of this neurotoxic metal, its concentration in drinking water is rarely regulated.

OBJECTIVE

We aimed to apply a benchmark concentration analysis to estimate water manganese levels associated with pre-defined levels of cognitive impairment in children, i.e. drop of 1%, 2% and 5% in Performance IQ scores.

METHODS

Data from two studies conducted in Canada were pooled resulting in a sample of 630 children (ages 5.9-13.7 years) with data on tap water manganese concentration and cognition, as well as confounders. We used the Bayesian Benchmark Dose Analysis System to compute weight-averaged median estimates for the benchmark concentration (BMC) of manganese in water and the lower bound of the credible interval (BMCL), based on seven different exposure-response models.

RESULTS

The BMC for manganese in drinking water associated with a decrease of 1% Performance IQ score was 133 μg/L (BMCL, 78 μg/L); for a decrease of 2%, this concentration was 266 μg/L (BMCL, 156 μg/L) and for a decrease of 5% it was 676 μg/L (BMCL, 406 μg/L). In sex-stratified analyses, the manganese concentrations associated with a decrease of 1%, 2% and 5% Performance IQ in boys were 185, 375 and 935 μg/L (BMCLs, 75, 153 and 386 μg/L) and 78, 95, 192 μg/L (BMCLs, 9, 21 and 74 μg/L) for girls.

CONCLUSION

Studies suggest that a maximum acceptable concentration for manganese in drinking water should be set to protect children, the most vulnerable population, from manganese neurotoxicity. The present risk analysis can guide decision-makers responsible for developing these standards.

Toenail manganese as biomarker of drinking water exposure: a reliability study from a US pregnancy cohort

Manganese (Mn) is an essential nutrient; however, overexposure can be neurotoxic. Recent evidence suggests that exposure to Mn from drinking water could be neurotoxic; however, research is hampered by the lack of consensus on a reliable biomarker of Mn exposure. Naturally high concentrations of Mn can occur in groundwater, particularly for private, unregulated water systems. This study aimed to investigate the association between exposure to Mn from drinking water with a relatively low Mn content (median of 2.9 μg/L; range, undetectable-8,340 μg/L) and Mn in toenails from women collected at two time points: during and after pregnancy. Mn concentrations in the paired toenail samples gathered during the second to third trimester of pregnancy and 2 weeks postpartum were correlated (r = 0.47, p < 0.001, n = 596). Among women consuming drinking water Mn in the highest tertile (i.e., > 9.8 μg/L) significant positive correlations were found between water Mn and toenails Mn (r = 0.31 and r = 0.38, for toenail samples collected during pregnancy and postpartum, respectively), whereas little to no correlation was observed at lower water concentrations. Overall, our data suggest that maternal toenail samples are a reliable environmental Mn exposure biomarker and reflect exposure from drinking water.

Assessing children's exposure to manganese in drinking water using a PBPK model

A previously published human PBPK model for manganese (Mn) in infants and children has been updated with Mn in drinking water as an additional exposure source. Built upon the ability to capture differences in Mn source-specific regulation of intestinal uptake in nursing infants who are breast-fed and formula-fed, the updated model now describes the bioavailability of Mn from drinking water in children of ages 0-18. The age-related features, including the recommended age-specific Mn dietary intake, age-specific water consumption rates, and age-specific homeostasis of Mn, are based on the available human data and knowledge of the biology of essential-metal homeostasis. Model simulations suggest that the impact of adding drinking-water exposure to daily Mn exposure via dietary intake and ambient air inhalation in children is not greater than the impacts in adults, even at a drinking-water concentration that is 2 times higher than the USEPA's lifetime health advisory value. This conclusion was also valid for formula-fed infants who are considered at the highest potential exposure to Mn from drinking water compared to all other age groups. Our multi-route, multi-source Mn PBPK model for infants and children provides insights about the potential for Mn-related health effects on growing children and will thereby improve the level of confidence in properly interpreting Mn exposure-health effects relationships in children in human epidemiological studies.

Hybrid Hollow Fiber Nanofiltration-Calcite Contactor: A Novel Point-of-Entry Treatment for Removal of Dissolved Mn, Fe, NOM and Hardness from Domestic Groundwater Supplies

Groundwater (GW) is one of the main potable water sources worldwide. However, the presence of undesirable compounds and particularly manganese (Mn) and iron (Fe) (mainly co-existing in GWs) are considered as objectionable components of potable water for both health and aesthetic issues. As such, individual dwellings supplied by domestic wells are especially threatened by these issues. Current domestic treatment technologies are complicated to operate and even dangerous if improperly maintained (e.g., catalytic filtration) or consume salts and produce spent brine which pollutes the environment (i.e., ion exchange resins). Therefore, it is of prime importance to design a simple and compact, yet robust, system for Mn and Fe control of the domestic GW sources, which can reliably guarantee the desired Mn limit in the finished water (20μg/L). In the course of this study, we demonstrated, for the first time, that a hybrid hollow fiber nanofiltration (HFNF)–calcite contactor process is a promising alternative for treating domestic GWs with elevated levels of Mn, Fe, natural organic matter (NOM) and hardness. The efficacy of the HFNF membranes in terms of removal of Mn, Fe, NOM and fouling was compared with commercially available NF270 and NF90 membranes. The results revealed that HFNF (100–200 Da) and NF90 maintained considerably high rejection of Mn, Fe and NOM due to their dominant sieving effect. In contrary, the rejections of the above-mentioned components were decreased in the presence of high hardness for the looser HFNF (200–300 Da) and NF270 membranes. No membrane fouling was detected and the permeate flux was stable when the hard GW was filtered with the HFNF membranes, regardless of their molecular weight cut-off and transmembrane pressure, while the permeability of the NF270 and NF90 membranes steadily decline during the filtration. Integrating a calcite contactor, as a post filtration step, to the HFNF process yielded further Mn, Fe and NOM removals from the HFNF permeate and adjustment of its hardness level. The best performance was achieved when a blend of Calcite–CorosexTM (90/10wt.%) was used as a post-treatment to the tight HFNF (100–200 Da).

Dietary Manganese Exposure in the Adult Population in Germany-What Does it Mean in Relation to Health Risks?

Manganese is both an essential nutrient and a potential neurotoxicant. Therefore, the question arises whether the dietary manganese intake in the German population is on the low or high side. Results from a pilot total diet study in Germany presented here reveal that the average dietary manganese intake in the general population in Germany aged 14-80 years is about 2.8 mg day^-1 for a person of 70 kg body weight. This exposure level is within the intake range of 2-5 mg per person and day as recommended by the societies for nutrition in Germany, Austria, and Switzerland. No information on the dietary exposure of children in Germany can be provided so far. Although reliable information on health effects related to oral manganese exposure is limited, there is no indication from the literature that these dietary intake levels are associated with adverse health effects either by manganese deficiency or excess. However, there is limited evidence that manganese taken up as a highly bioavailable bolus, for example, uptake via drinking water or food supplements, could pose a potential risk to human health-particularly in certain subpopulations-when certain intake amounts, which are currently not well defined, are exceeded.

Verbal Memory and Learning in Schoolchildren Exposed to Manganese in Mexico

Manganese (Mn) is an essential nutrient for cellular function, but in high concentrations, it is neurotoxic. Environmental exposure to Mn has been associated with cognitive effects in children. This study aimed to assess the effect of environmental exposure to Mn on verbal memory and learning in schoolchildren residents from two municipalities in the state of Hidalgo, Mexico. Cross-sectional studies were conducted in 2006 and 2013 with a total of 265 schoolchildren of 7 to 11 years old. Children's Auditory Verbal Learning Test-2 (CAVLT-2) was used to assess verbal memory and learning. Mn exposure tertiles were defined according to hair manganese (MnH) levels determined by atomic absorption spectrophotometry. Linear regression models were used to estimate the association between MnH levels and CAVLT-2 scores. The models were adjusted by potential confounders. The lowest and highest exposure tertiles were defined below and above MnH levels of ≤ 0.72 and ≥ 3.96 μg/g, respectively. Mn exposure was significantly associated with an average of 5- to 9-point decrease in learning curves and summary CAVLT-2 scores in the highest tertile. This study adds to the evidence of decreased verbal memory and learning in schoolchildren environmentally exposed to manganese.

[Investigation of the Effects of Exposure to Chemical Substances on Child Health]

There is mounting concern about the effects of early-life exposure to chemical substances on children's health and development. We summarize the past and ongoing birth cohort studies carried out worldwide on the association between environmental exposure and children's health. Our PubMed search with the keywords 'birth cohort' revealed that the number of articles jumped from 200-300 in the 1980s to over 1,000 in the 1990s. Many of these articles reported elevated risks to children's health posed by chemical exposure owing their vulnerability. At the same time, policies implemented to reduce exposure to lead and dioxins were successful in the past few decades. Research also demonstrated that intervention to reduce exposure to certain chemicals whose exposure routes were well documented was also successful. We summarize the effects of early-life exposure to chemical substances on children's health and development. Our findings will hopefully help safeguard the environment in which future generations grow and live.

A systematic literature review of epidemiologic studies of developmental manganese exposure and neurodevelopmental outcomes

BACKGROUND

Neurotoxic effects of high-level occupational exposure to manganese (Mn) are well established; however, whether lower-level environmental exposure to Mn in early life causes neurodevelopmental toxicity in children is unclear.

METHODS

A systematic literature review was conducted to identify and evaluate epidemiologic studies of specific Mn biomarkers assessed during gestation, childhood, or adolescence in association with neurodevelopmental outcomes, focusing on quantitative exposure-response estimates with specific endpoints that were assessed in multiple independent study populations. Study quality was evaluated using the revised RTI item bank and the Cochrane Risk of Bias tool, and the overall weight of epidemiologic evidence for causality was evaluated according to the Bradford Hill considerations.

RESULTS

Twenty-two epidemiologic studies were identified that estimated associations between early-life Mn biomarkers and neurodevelopmental outcomes. Seven of these studies provided adjusted estimates for the association with child intelligence assessed using versions of the Wechsler Intelligence Scales for Children; no other specific neurodevelopmental endpoints were assessed in more than three independent study populations each. Among the studies of child intelligence, five studies in four independent populations measured blood Mn, three studies measured hair Mn, and one measured dentin Mn. Overall, cross-sectional associations between Mn biomarkers and measures of child intelligence were mostly statistically nonsignificant but in a negative direction; however, the lone prospective cohort study found mostly null results, with some positive (favorable) associations between dentin Mn and child intelligence. Studies were methodologically limited by their cross-sectional design and potential for confounding and selection bias, as well as unaddressed questions on exposure assessment validity and biological plausibility.

CONCLUSIONS

The statistical associations reported in the few studies of specific Mn biomarkers and specific neurodevelopmental endpoints do not establish causal effects based on the Bradford Hill considerations. Additional prospective cohort studies of Mn biomarkers and validated neurodevelopmental outcomes, and a better understanding of the etiologic relevance of Mn biomarkers, are needed to shed light on whether environmental exposure to Mn causes adverse neurodevelopmental effects in children.

Iron and manganese-related CNS toxicity: mechanisms, diagnosis and treatment

INTRODUCTION

Iron (Fe) and manganese (Mn) are essential nutrients for humans. They act as cofactors for a variety of enzymes. In the central nervous system (CNS), these two metals are involved in diverse neurological activities. Dyshomeostasis may interfere with the critical enzymatic activities, hence altering the neurophysiological status and resulting in neurological diseases. Areas covered: In this review, the authors cover the molecular mechanisms of Fe/Mn-induced toxicity and neurological diseases, as well as the diagnosis and potential treatment. Given that both Fe and Mn are abundant in the earth crust, nutritional deficiency is rare. In this review the authors focus on the neurological disorders associated with Mn and Fe overload. Expert commentary: Oxidative stress and mitochondrial dysfunction are the primary molecular mechanism that mediates Fe/Mn-induced neurotoxicity. Although increased Fe or Mn concentrations have been found in brain of patients, it remains controversial whether the elevated metal amounts are the primary cause or secondary consequence of neurological diseases. Currently, treatments are far from satisfactory, although chelation therapy can significantly decrease brain Fe and Mn levels. Studies to determine the primary cause and establish the molecular mechanism of toxicity may help to adapt more comprehensive and satisfactory treatments in the future.

Manganese levels in newborns' hair by maternal sociodemographic, dietary and environmental factors

Exposure to manganese (Mn) has been associated with neurodevelopmental problems in children. Mn exposure begins in utero, and maternal sociodemographic, dietary and environmental factors may affect Mn levels in newborns' hair. This study aimed to characterize in utero Mn exposure using Mn levels in newborns' hair as a biomarker of prenatal exposure, and to analyze its relationship with sociodemographic, dietary and environmental factors in the Spanish INMA-Gipuzkoa cohort. Overall, 638 pregnant women were recruited in the first trimester of pregnancy and a hair sample was obtained from 473 newborns. Sociodemographic, dietary and environmental data were recorded through two questionnaires administered in the first and third trimesters of pregnancy. The median Mn concentration in newborns´ hair was 0.31 µg/g (P5 = 0.02; P95 = 1.23). Mn levels in newborns´ hair were associated with smoking during pregnancy (β = 0.222; 95% CI = 0.065-0.379) and with maternal PM_2.5 exposure (β = 0.025; 95% CI = 0.004; 0.047), as well as with cereal and pasta intake in the first trimester of pregnancy (β = 0.002; 95% CI = 0.0004; 0.003). In conclusion, fetal exposure to Mn was associated with smoking and exposure to atmospheric pollution during pregnancy.

The effects of manganese exposure from drinking water on school-age children: A systematic review

The aim of this study was to analyse the published literature on the potential effects of manganese exposure from drinking water on school-age children, with emphasis on cognitive, and neurodevelopment and behavioural effects. A systematic review of up-to-date scientific evidence published from 2006 to 2017 was conducted using Science Direct. A further search was carried out using PubMed and Web of Science. A total of 21 studies were reviewed and categorised into 12 cognitive and 9 neurodevelopment and behavioural effects. The most utilised cognitive test was the Wechsler Intelligence Scale for Children (WISC) or some subtests from it. 10 of the 12 studies on cognitive effects reported an adverse effect of manganese exposure from drinking water on children. 3 out of the 9 studies on neurodevelopment and behavioural effects reported that manganese exposure from drinking water was associated with poorer neurobehavioural performances in school children. 4 others implied the presence of some sex-specific associations with manganese exposure. 1 study suggested that children suffering from attention deficit hyperactivity disorder (ADHD) may be more susceptible to manganese exposure. Another study suggested that manganese was a beneficial nutrient as well as a neurotoxicant. Regardless of the limitations of the studies analysed, the adverse effects of manganese exposure from drinking water on school-aged children is sufficiently demonstrated. Further investigation into the subject to address inconsistencies in existing studies is recommended.

In vitro antioxidant, anti-glycation and immunomodulation activities of fermented blue-green algae Aphanizomenon flos-aquae

To clarify the antioxidant, anti-glycation and immunomodulatory capacities of fermented blue-green algae Aphanizomenon flos-aquae (AFA), hot aqueous extract suspensions made from 10% AFA were fermented by Lactobacillus plantarum AN7 and Lactococcus lactis subsp. lactis Kushiro-L2 strains isolated from a coastal region of Japan. The DPPH and O₂^- radical scavenging capacities and Fe-reducing power were increased in the fermented AFA. The increased DPPH radical scavenging capacity of the fermented AFA was fractionated to mainly < 3 kDa and 30-100 kDa. The increased O₂^- radical scavenging capacities were fractionated to mainly < 3 kDa. Anti-glycation activity in BSA-fructose model rather than BSA-methylglyoxal model was increased by the fermentation. The increased anti-glycation activity was fractionated to mainly 30-100 kDa. The NO concentration in the murine macrophage RAW264.7 culture media was high with the fermented AFA. The increased immunomodulation capacity was also fractionated to mainly 30-100 kDa. These results suggest that the fermented AFA is a more useful material for health foods and supplements.

Metal bashing: iron deficiency and manganese overexposure impact on peripheral nerves

Iron (Fe) deficiency (FeD) and manganese (Mn) overexposure (MnOE) may result in several neurological alterations in the nervous system. Iron deficiency produces unique neurological deficits due to its elemental role in central nervous system (CNS) development and myelination, which might persist after normalization of Fe in the diet. Conversely, MnOE is associated with diverse neurocognitive deficits. Despite these well-known neurotoxic effects on the CNS, the influence of FeD and MnOE on the peripheral nervous system (PNS) remains poorly understood. The aim of the present investigation was to examine the effects of developmental FeD and MnOE or their combination on the sciatic nerve of young and adult rats. The parameters measured included divalent metal transporter 1 (DMT1), transferrin receptor (TfR), myelin basic protein (MBP) and peripheral myelin protein 22 (PMP22) expression, as well as Fe levels in the nerve. Our results showed that FeD produced a significant reduction in MBP and PMP22 content at P29, which persisted at P60 after Fe-sufficient diet replenishment regardless of Mn exposure levels. At P60 MnOE significantly increased sciatic nerve Fe content and DMT1 expression. However, the combination of FeD and MnOE produced no marked motor skill impairment. Evidence indicates that FeD appears to hinder developmental peripheral myelination, while MnOE may directly alter Fe homeostasis. Further studies are required to elucidate the interplay between these pathological conditions.

SLC30A10 transporter in the digestive system regulates brain manganese under basal conditions while brain SLC30A10 protects against neurotoxicity

The essential metal manganese becomes neurotoxic at elevated levels. Yet, the mechanisms by which brain manganese homeostasis is regulated are unclear. Loss-of-function mutations in SLC30A10, a cell surface-localized manganese efflux transporter in the brain and liver, induce familial manganese neurotoxicity. To elucidate the role of SLC30A10 in regulating brain manganese, we compared the phenotypes of whole-body and tissue-specific Slc30a10 knockout mice. Surprisingly, unlike whole-body knockouts, brain manganese levels were unaltered in pan-neuronal/glial Slc30a10 knockouts under basal physiological conditions. Further, although transport into bile is a major route of manganese excretion, manganese levels in the brain, blood, and liver of liver-specific Slc30a10 knockouts were only minimally elevated, suggesting that another organ compensated for loss-of-function in the liver. Additional assays revealed that SLC30A10 was also expressed in the gastrointestinal tract. In differentiated enterocytes, SLC30A10 localized to the apical/luminal domain and transported intracellular manganese to the lumen. Importantly, endoderm-specific knockouts, lacking SLC30A10 in the liver and gastrointestinal tract, had markedly elevated manganese levels in the brain, blood, and liver. Thus, under basal physiological conditions, brain manganese is regulated by activity of SLC30A10 in the liver and gastrointestinal tract, and not the brain or just the liver. Notably, however, brain manganese levels of endoderm-specific knockouts were lower than whole-body knockouts, and only whole-body knockouts exhibited manganese-induced neurobehavioral defects. Moreover, after elevated exposure, pan-neuronal/glial knockouts had higher manganese levels in the basal ganglia and thalamus than controls. Therefore, when manganese levels increase, activity of SLC30A10 in the brain protects against neurotoxicity.

Toenail manganese as a potential biomarker for in utero and early childhood exposure studies

Elevated in utero and early childhood exposure to manganese may have adverse effects on neurodevelopment. We conducted preliminary analyses to evaluate toenails as a matrix for investigating manganese exposure in infants. Infant and maternal toenail and hair samples were collected from 25 infants (7 months old) and their mothers. A subset of mothers was recruited in the third trimester of pregnancy and some also provided pre-natal toenail, hair, and blood samples, cord blood, and additional post-natal samples. Collected samples were analyzed by inductively coupled plasma mass-spectrometry. Toenail manganese levels in infants ranged from below the limit of detection (LOD) to 2.80 µg/g. Only 1 toenail sample and 4 hair samples contained levels of manganese below LOD. Associations between infant and maternal biomarkers were not statistically significant. Analysis of multiple post-natal toenail samples from a single infant-mother pair showed an increase in the infant’s toenail manganese and a decrease in maternal toenail manganese over the first year of the infant’s life. Overall, our findings suggest that toenails may serve as a valuable biological matrix for measuring manganese exposure in newborns and infants; however, additional studies are needed to determine the impact of the timing of toenail sample collection on its utility in assessing early life exposure and health outcomes.

Performance of thin-film composite hollow fiber nanofiltration for the removal of dissolved Mn, Fe and NOM from domestic groundwater supplies

Groundwater (GW) is one of the most abundant water resources and around 1.5 billion people rely on GW as their main water supply. Manganese (Mn) and iron (Fe) are very common GW contaminants. Even though their presence is considered mainly as an organoleptic and operational nuisance, water with elevated Mn content may also lead to adverse health impacts. Amongst the most common treatment processes currently used to treat domestic GW supplies: catalytic filtration may lead to Mn leaching if improperly maintained; while ion exchange consumes a considerable amount of salt and produces a brine waste which pollutes the environment. Thus, it is proposed to design a simple, yet robust treatment system which can be implemented in small/remote communities or even domestic applications. To this end, the main objective of this investigation was to assess the potential application of novel outside-in sulfonated polyethersulfone thin-film composite hollow fiber nanofiltration (HFNF) membranes to remove dissolved Mn, Fe and natural organic matter (NOM) from domestic GW supplies. Of particular interest was the impact of GW matrix on performance of the HFNF membranes. Our experimental findings demonstrated that, in absence of hardness and the cumulative throughput of 1.9 L/m², above 90% of Mn, Fe and NOM were retained by the examined HFNF membranes (MWCO ∼ 200 Da) regardless of their initial concentrations in the feed solution (250-1000 μ g/L). In contrast, increasing the hardness level reduced the removal of Mn and Fe ions. XPS analysis revealed that the surface properties of the HFNF membranes were altered when the membranes were exposed to calcium and magnesium salts. These observations were attributed to the propensity for Ca and Mg ions to bind to the sulfonic groups present on the surface of the HFNF membranes which, subsequently, weakens rejection by charge exclusion. On the other hand, in the absence of GW hardness, charge exclusion was mainly responsible for rejection of dissolved Mn and Fe. It was also found that GW hardness had no marked impact on the NOM rejection as the later was mostly removed by size exclusion.